1. Field of the Invention
The present invention relates to a PCB terminal mostly used in electric wirings of automobiles and other consumer devices and a method for manufacturing the PCB terminal, more particularly to a PCB terminal required to fulfill the demands for friction and wear reduction when inserted in and pulled out from a female terminal in a fitting portion and also required to have good solderability to a circuit board in a soldering portion, and a method for manufacturing such a PCB terminal.
2. Description of Related Art
PCB connectors are often used in ECU (engine control unit) of automobiles and electronic control circuit boards of consumer devices. The PCB connector serves to connect PCB (printed circuit board) and a female connector including female terminals. The PCB connector is embedded with a large number of PCB terminals. The PCB terminal includes a fitting portion on one end, a soldering portion provided on the other end, and an intermediate portion situated between the fitting portion and the soldering portion. Conventionally, the PCB terminals are inserted in a predetermined number of insertion holes formed in a box-shaped cabinet made of resin, and the cabinet is immovably set at intermediate portions of the PCB terminals to be used as a PCB connector. The fitting portions of the PCB terminals are fitted in the female terminals housed in the female connector. The soldering portions of the PCB terminals are inserted in through holes formed in the printed circuit board and soldered thereto.
International Publication WO2008-072418 discloses a PCB terminal wherein a surface coating layer made of Ni plating layer/Cu—Sn alloy layer/Sn plating layer (in the mentioned order from the side of materials, the same shall apply hereinafter) is formed on the fitting portion, a surface coating layer made of Ni plating layer/Sn—Ni alloy layer/Sn plating layer is formed on the soldering portion, and a surface coating layer made of one of an Ni plating layer, an Ni—Sn alloy layer, and a Cu—Sn alloy layer is formed on the intermediate portion. When the surface coating layers are thus provided, the fitting portion can achieve a low contact resistance and a low insertion and extraction force, the soldering portion can provide favorable solderability, and the intermediate portion can effectively prevent occurrence of solder wicking. International Publication WO2008-072418 also discloses a manufacturing method wherein a base material is die-cut into a predetermined terminal shape, and the fitting portion, soldering portion, and intermediate portion are then respectively subjected to after-plating as required and then subjected to a reflow treatment.
Japanese Unexamined Patent Publication No. 05-82201 discloses a terminal constituting a conventional surface mounting connector wherein the terminal is formed in a substantially L shape and has a semi-circular bent portion at an upper end thereof. An upper-end side is a contact portion, while a lower-end side thereof is a portion to be connected to a circuit board. When the contact portion elastically contacts another terminal and the portion to be connected to the circuit board is soldered to the circuit board, the terminal is electrically connected to another terminal or the circuit board. A base material of the terminal is copper or copper alloy, the contact portion is provided with a contact coating film made of metal selected from Au, Sn, solder and the like, the portion to be connected to the circuit board is provided with a metallic coating film constituting a soldering portion including Sn or solder, and these metallic coating films are often formed with an undercoat metallic film including Cu or Ni interposed therebelow as a barrier layer which prevents diffusion of the material into the base material. Referring to FIG. 6 of Japanese Unexamined Patent Publication No. 05-82201 illustrating the terminal, a metallic undercoat is formed between the contact portion and the portion to be connected to the circuit board.
Japanese Patent No. 3926355 discloses an electrically conductive material for connecting parts having high electrical reliability (low contact resistance) and a small coefficient of friction, which is suitably used as a matable connector terminal. According to the invention disclosed in Japanese Patent No. 3926355, a copper alloy strip having a larger surface roughness than conventional copper alloy strips is used as a base material, an Ni plating layer, a Cu plating layer and a Sn plating layer, or a Cu plating layer and a Sn plating layer are formed on the surface of the base material in the mentioned order, or a Sn plating layer alone is formed on the surface, and the Sn plating layer is subjected to the reflow treatment so that a Cu—Sn alloy layer is formed from the Cu plating layer and the Sn plating layer, or the copper alloy base material and the Sn plating layer, and a part of the Cu—Sn alloy layer is exposed on the surface through the Sn plating layer smoothened by the reflow treatment (a part of the Cu—Sn alloy layer is exposed on the surface of the base material through protrusions of an irregularity portion formed thereon).
The electrically conductive material for connecting parts formed after the reflow treatment, which is disclosed in Japanese Patent No. 3926355, has a surface coating layer including a Cu—Sn alloy layer and a Sn layer, or an Ni layer, a Cu—Sn alloy layer and a Sn layer in the mentioned order, and a Cu layer possibly remains between the surface of the base material and the Cu—Sn alloy layer or between the Ni layer and the Cu—Sn alloy layer. It is defined in Japanese Patent No. 3926355 that the Cu—Sn alloy layer and the Sn layer are formed as an outermost surface (area ratio of the Cu—Sn alloy layer exposed on the surface is 3 to 75%), the Cu—Sn alloy layer has an average thickness of 0.1 to 3.0 μm, a contained amount of Cu is 20 to 70 at %, and the Sn layer has an average thickness of 0.2 to 5.0 μm. It is further disclosed in Japanese Patent No. 3926355 that an arithmetic mean roughness Ra of the base material surface in at least one direction is desirably at least 0.15 μm, the arithmetic mean roughness Ra thereof in all of directions is desirably at most 4.0 μm, and the Cu—Sn alloy layer is desirably exposed on the surface at intervals of 0.01 to 0.5 mm in at least one direction.
Japanese Patent No. 4024244 discloses an electrically conductive material for connecting parts equivalent to a subordinate concept of Japanese Patent No. 3926355, and a manufacturing method thereof, wherein a plating layer and a post-reflow coating layer itself are configured equally to those disclosed in Japanese Patent No. 3926355. In the electrically conductive material for connecting parts formed after the reflow treatment which is disclosed in Japanese Patent No. 4024244, a Cu—Sn alloy layer and a Sn layer are formed as an outermost surface (Cu—Sn alloy layer of the surface coating layer has an exposure area ratio from 3 to 75%), wherein it is defined that the Cu—Sn alloy layer has an average thickness of 0.2 to 3.0 μm, a contained amount of Cu is 20 to 70 at %, the Sn layer has an average thickness of 0.2 to 5.0 μm, an arithmetic mean roughness Ra of the material surface in at least one direction is at least 0.15 μm, and the arithmetic mean roughness Ra thereof in all of directions is at most 3.0 μm. It is further disclosed in Japanese Patent No. 4024244 that an arithmetic mean roughness Ra of the base material surface in at least one direction is desirably at least 0.3 μm, the arithmetic mean roughness Ra thereof in all of directions is desirably at most 4.0 μm, and the Cu—Sn alloy layer is desirably exposed on the surface at an interval of 0.01 to 0.5 mm in at least one direction.
Japanese Unexamined Patent Publication No. 2007-258156 discloses an electrically conductive material for connecting parts which achieves better solderability while essentially succeeding the technical ideas of Japanese Patent Nos. 3926355 and 4024244, and a manufacturing method thereof. Although a plating layer and a post-reflow coating layer itself according to the invention disclosed in this document are basically configured equally to those disclosed in Japanese Patent Nos. 3926355 and 4024244, a Cu—Sn alloy layer according to the invention may not be exposed (outermost surface may include Sn layer alone), which is different from Japanese Patent Nos. 3926355 and 4024244. In the electrically conductive material for connecting parts formed after the reflow treatment which is described in the subject application, an Ni layer of the surface coating layer has an average thickness equal to or smaller than 3.0 μm, the Cu—Sn alloy layer of the surface coating layer has an average thickness of 0.2 to 3.0 μm, a minimum inscribed circle diameter “D1” of the Sn layer in a perpendicular cross section of the material is equal to or smaller than 0.2 μm, a maximum inscribed circle diameter “D2” thereof is equal to or smaller than 1.2 to 20 μm, and a height difference “Y” between an outermost point of the material and an outermost point of the Cu—Sn alloy layer is equal to or smaller than 0.2 μm. It is further disclosed that a maximum inscribed circle diameter “D3” of the Cu—Sn alloy layer on the material surface is desirably equal to or smaller than 150 μm and/or a maximum inscribed circle diameter “D4” of the Sn layer on the material surface is desirably equal to or smaller than 300 μm when “D1” is 0 μm (a part of the Cu—Sn alloy layer is exposed on a surface of the base material, and the outermost surface includes the Cu—Sn alloy layer and the Sn layer).
It is disclosed in Japanese Unexamined Patent Publication Nos. 2004-300524, 2005-105307, and 2005-183298 that when a copper alloy strip is subjected to die cutting work and then plated with Sn in whole, in other words, subjected to after-plating so that a Sn plating layer is formed on not only a rolled surface but also a die-cut end surface, a terminal thereby obtained can have better solderability than a terminal obtained by plating the copper alloy strip with Sn before the die cutting work (pre-plating).
Japanese Unexamined Patent Publication Nos. 2008-269999 and 2008-274364 disclose a terminal subjected to after-plating which achieves higher electric reliability (low contact resistance), a small coefficient of friction in the fitting portion, and a solderability improvement in the soldering portion.
According to the invention disclosed in Japanese Unexamined Patent Publication No. 2008-269999, the fitting portion alone has an increased surface roughness when the terminal is formed, an Ni plating layer, a Cu plating layer, and a Sn plating layer are formed in the mentioned order, or the Cu plating layer and the Sn plating layer are formed in the mentioned order, or the Sn plating layer alone is formed on the fitting portion, the Sn plating layer is subjected to the reflow treatment so that the Cu—Sn alloy layer is formed from the Cu plating layer and the Sn plating layer, or the copper alloy base material and the Sn plating layer, and a part of the Cu—Sn alloy layer is exposed on the surface of the base material through the Sn plating layer smoothened by the reflow treatment (a part of the Cu—Sn alloy layer is exposed on the base material surface through protrusions of an irregularity portion formed thereon). A plating thickness is equal on all of the surfaces. Although the fitting portion, where the Cu—Sn alloy layer and the Sn layer are formed as an outermost surface (Cu—Sn alloy layer is exposed on the surface), may have a problem in its solderability, portions having no irregularity other than the fitting portion where the Cu—Sn alloy layer is not exposed (outermost surface is Sn layer alone) have favorable solderability.
According to the invention disclosed in Japanese Unexamined Patent Publication No. 2008-274364, die cutting work is performed to a copper alloy material having a large surface roughness to obtain a terminal material, an Ni plating layer, a Cu plating layer and a Sn plating layer are formed in the mentioned order, or the Cu plating layer and the Sn plating layer are formed in the mentioned order, or the Sn plating layer alone is formed, the Sn plating layer is subjected to the reflow treatment so that the Cu—Sn alloy layer is formed from the Cu plating layer and the Sn plating layer, or the copper alloy base material and the Sn plating layer, and a part of the Cu—Sn alloy layer is exposed on a surface of the base material through the Sn plating layer smoothened by the reflow treatment (a part of the Cu—Sn alloy layer is exposed on the base material surface through protrusions of an irregularity portion formed thereon). The Sn plating layer of the soldering portion is formed in a large thickness so that the Cn—Sn alloy layer is not exposed on the surface in the soldering portion. Therefore, the soldering portion can ensure favorable solderability.
The fitting portion of the PCB terminal disclosed in International Publication WO2008-072418, where the hard Cu—Sn alloy layer is present below Sn of the surface layer, essentially has a smaller coefficient of friction than conventional post-reflow Sn-plated material. The reduction of the coefficient of friction in the PCB terminal, however, is not as effective as in the terminals produced from the materials of Japanese Patent Nos. 3926355 and 4024244 or the terminals disclosed in Japanese Unexamined Patent Publication Nos. 2008-269999 and 2008-274364.
The electrical conductive materials for connecting parts disclosed in Japanese Patent Nos. 3926355 and 4024244, and Japanese Unexamined Patent Publication Nos. 2007-258156, 2008-269999, and 2008-274364 are characterized in that the surface-roughened copper plate is used as the base material, the Ni plating layer, Cu plating layer and Sn plating layer, for example, are formed in the mentioned order on the surface of the base material, the Sn plating layer is subjected to the reflow treatment, the Cu—Sn alloy coating layer is formed from the Cu plating layer and the Sn plating layer, and a part of the Cu—Sn alloy coating layer is exposed on the surface through the Sn coating layer smoothened by the reflow treatment.
Conventionally, there are parameters representing exposure statuses of the Sn coating layer and the Cu—Sn coating layer, which are: the exposure area ratio and the average exposure intervals of the Cu—Sn alloy coating layer (Japanese Patent Nos. 3926355 and 4024244), and the maximum inscribed circle diameter and the maximum circumscribed circle diameter of the Sn coating layer (Japanese Unexamined Patent Publication No. 2007-258156).
However, no notice has been taken so far for shapes of the Sn coating layer and the Cu—Sn alloy coating layer. To meet the demand for further downsizing of the terminal, it is recommended to start addressing specific shapes of the Sn coating layer and the Cu—Sn alloy coating layer rather than simply relying on the relatively unspecific parameters conventionally available, because it will soon be necessary to provide these layers with a planar shape which is suitably controllable and easy to form.
Therefore, the present invention provides a PCB terminal provided with a Sn coating layer and a Cu—Sn alloy coating layer having a suitably controllable planar shape in the fitting portion, and having a small coefficient of friction and remarkable electrical reliability (low contact resistance value after prolonged heating) that can meet the demand for further downsizing.